A component of this type is known from the essay "New type of thin film colour image sensor", Q. ZHU, H. Stiebig, P. Rieve, J. Giehl, M. Sommer, M. Bohm; Conference Europto--Sensors and Control for Advanced Automation II, Frankfurt/Main, 20-24 June 1994.
Compared with components of crystalline silicon, photo sensitive electronic components based on amorphous silicon (a-Si:H) have the advantage of significantly increased absorption of visible light. Basically such a photo sensitive electronic component consists of two PIN diodes connected antiserially in respect to each other, whereby the alternatives NIPIN or PINIP are known; or of two metal-semiconductor junctions (Schottky contacts) connected to each other antiserially.
Technologically, such a component is produced by separating a multitude of a-Si:H layers at low temperature (typically 250.degree. C.) by means of the PECVD (Plasma Enhanced Chemical Vapour Deposition) process. Deposition takes place at first for example on an insulating substrate, usually glass, by connecting a translucent conductive oxide layer (TCO) which later establishes a contact for an electrical voltage to be applied externally to the component. By applying an alternating field, a plasma is generated at the PECVD reactor by the gas SiH.sub.4 (silane) being decomposed into silicon radicals and hydrogen. In this process, silicon condenses on the substrate as an amorphous film containing hydrogen. Starting from this, by adding phosphine, an n-doped layer can be produced; or by adding boroethane, a p-doped layer can be produced. In addition, it is well known to increase the band gap of the amorphous silicon by adding methane (CH.sub.4) to the silane, or to decrease the band gap by adding germane (Ge H.sub.4)
The multilayer component produced in this way, having the desired layer sequence, is now penetrated by radiation of visible light in such a way that the direction of light incidence is perpendicular to the plane of the layers. Because the absorption coefficient of the sensor material depends on the wave length of the incoming light and on the band gap of the sensor material, different penetration depths of light into the semiconductor material results. This leads to blue light (wavelength approx. 450 nm) having a significantly lesser penetration depth (absorption length) than green or red light. By selecting the respective size and polarity of the exterior direct voltage applied to the component, and therefore the interior electrical field, a spectral sensitivity of the component can be attained. For example by applying respective voltages to the element, a sensitivity for RGB light (red, green, blue) in the multilayer structure can be attained. In this the principal collecting region of the light-generated charge carriers along the length of the component and consequently its spectral sensitivity, is shifted, depending on the exterior voltage applied.
In order to optimise a NIPIN structure in respect of a trichromatic sensor, it is known from the above-mentioned report, on both sides of the p-doped intermediate layer, to additionally provide intrinsically conducting defect layers in whose thickness region the band gap is increased in comparison to the remaining intrinsically conducting layers (e.g. from 1.74 eV to 1.9 eV). This leads to an improved red/green separation in the NIP structure in front in the direction of light incidence, or to an improved red/green separation in the subsequent PIN structure in the direction of light incidence, (so-called band-gap engineering).
From U.S. Pat. No. 5,311,047 a photo sensitive electronic component based on amorphous silicon with NIPIN structure is known.
From Applied Physics Letters 52(4) 1988, 275-277, a heterojunction component (phototransistor) of the type NIPIN is known which comprises two additionally-inserted intrinsically conducting layers. From this it is known that in the first junction preferably blue light, and in the second junction preferably green or red light, are absorbed. The second intrinsically conducting layer serves to increase blue absorption.
It is the object of the invention to describe an electronic component of the type mentioned in the introduction, as well as a method for its manufacture which ensures that under economic fabrication conditions a component sensitive to RGB colours is created which features a high spectral separation for RGB colours with negligible infrared/ultraviolet contributions to the output signal.